The present invention relates to a cutting, profiling, and edge-preparing apparatus and, more particularly, to an apparatus for cutting a pipe to be used, for instance, in a nuclear power plant, and/or for preparing an edge of the pipe for welding.
A cutting and edge-preparing apparatus has been used for cutting a pipe and preparing an edge of a pipe for welding. The conventional cutting and edge-preparing apparatus is mounted on an outer surface of a pipe, i.e., workpiece, to cut the pipe and to prepare the edge of the pipe for welding. The apparatus typically includes a stationary unit, a revolving unit, and cutting tools. The stationary unit is fixedly mounted on the pipe, and the revolving unit is mounted on a front surface of the stationary unit such that it can rotate about the outer surface of the pipe. A pin is fixed to the stationary unit so as to project radially inward.
The revolving unit holds a tool holder to which a plurality of tools are mounted. The tool holder is typically provided with a star wheel, and a tool feed screw is connected coaxially to the star wheel. The tools move radially outward or inward when the star wheel is turned.
The pin of the stationary unit and the star wheel provided with the tool holder constitute a tool feed mechanism. When the revolving unit revolves about the pipe, the star wheel collides against the radially-projecting pin. The star wheel is turned by the shock experienced due to the collision of the star wheel against the pin, and the screw connected to the star wheel feeds the tools. Thus, the star wheel collides against the pin as the revolving unit revolves about the pipe, and the star wheel turns little-by-little to feed the tools.
In the foregoing conventional cutting and edge-preparing apparatus, the tools are fed by the collision of the star wheel against the pin. Consequently, the star wheel comes into contact with the pin and the star wheel is subjected to shocks generated by the collision when the apparatus operates. Accordingly, the operator of the apparatus is in danger of being caught in the moving and contacting parts of the apparatus. Moreover, there is a possibility that the revolving unit will fall off the apparatus due to the impact of the collisions and shocks, and machining accuracy is reduced.
Sometimes, the star wheel of the tool feed mechanism may fail to turn when the star wheel collides with the pin and, consequently, the tools held by the plurality of tool holders are not fed at the same rate. Further, the tool feed mechanism including the star wheel is utilized to feed the tools to the pipe and to return the tools to their home positions via the collisions of the star wheel with the pin. Thus, the tool feed mechanism of the conventional apparatus is unable to feed the tools in a rapid-feed mode and/or to return the tools in a rapid-return mode. Accordingly, it takes a long time to engage the tools with the outer surface of the pipe at the start of an operation, and the tools are returned to their home positions after the completion of a cutting operation in an amount of time that is equal to the time spent for the cutting operation.
In an alternative procedure, tool holders may be manually and individually returned to their home positions by the operator to curtail the time typically necessary for returning the tools to their home positions. When tool holders are returned to their home positions manually by the operator, the tool holders require re-mounting on the apparatus before the next cutting operation can begin. However, it is difficult to accurately mount the tool holders on the apparatus. The tools held by the two tool holders are required to be located at identical radial positions, respectively. The allowable range of error in the amount of radial projection of the tools is on the order of ±0.2 mm. A cutting edge of a tool that has a greater amount of radial projection than that of the other is subjected to greater loading, and it is possible that the tool will break unless errors in the respective amounts of radial projection of the tools are adjusted to within the above referenced allowable tolerances. Therefore, it is important that tool holders be accurately mounted on the apparatus.
In cutting a pipe and forming a groove in an edge of the pipe at a job site, the tool feed mechanism including the star wheel feeds the tools by a fixed feed upon the contact of the star wheel with the pin. Therefore, a large load is placed on the apparatus upon the impact of the star wheel on the pin and, sometimes, the apparatus becomes dislocated. Consequently, machining accuracy is reduced, roughness of the machined surface increases, and a stripe formed in a part of the circumference of the pipe at the completion of machining causes faulty welding. This unavoidably causes the need to change welding work and welding conditions.
In addition to cutting pipe, profile machining apparatus is also required to prepare an edge of a cut pipe. For example, in a nuclear power plant or like facilities, pipe connections are made by welding operations or the like, and this requires the edges of the pipes to be specially prepared or profiled.
Generally, as illustrated in FIGS. 21A, 21B and 21C, an inner surface grinding section 196, a recess 194, a lip 190, and a groove 192 are formed in the edges of each pipe being prepared for connection by a welding operation. Various groove shapes are utilized including, for instance, a single U-shaped groove as shown in FIG. 21A, a single V-shaped groove as shown in FIG. 21B, and a double bevel groove as shown in FIG. 21C. Typically, the desired shape of an edge of a pipe is determined according to wall material, wall thickness, and welding method.
As shown in FIG. 22A, a tool 186 of a conventional edge preparing apparatus is manually or automatically moved in a radial direction of a pipe “P” so as to form a lip 190 and a groove 192 in an outer edge of the pipe “P”. In either case of manual or automatic operation, a cutting direction is limited to a direction along one axis. Therefore, when wall thickness or groove angle of a pipe “P” is large, a contact area of the tool 186 becomes very large, and the positioning of the entire apparatus relative to the pipe may be required to be changed. In this case, it is necessary to re-center the revolving unit and the pipe. In addition, since cutting volume is large, considerable skill is necessary for this operation and it is difficult to obtain satisfactory edge forming accuracy. When edge preparation is conducted on an outer surface of a pipe, it is especially difficult to control the thickness of the relatively thin lip of the desired edge profile.
Further, as shown in FIG. 22B, a tool 188 of a conventional edge-preparing apparatus is movable in a direction only along one axis (i.e., an axial direction of the pipe) to form an inner surface grinding section 196 and a recess 194 in an inner surface of the pipe “P” as well as that of FIG. 22A. Therefore, it is necessary to form a tool 188 according to the shape of the inner surface grinding section 196 and the recess 194 and place the tool 188 on an inner surface of the pipe “P” for the cutting operation. Therefore, when a machined area of an inner surface is large, a contact area of the tool 188 becomes very large at the part of the recess 194, and the position of the entire apparatus relative to the pipe may require frequent re-positioning. In this case, it is necessary to center the revolving unit and pipe repeatedly. In addition, since cutting volume is large, considerable skill is necessary for this operation, and it is difficult to obtain satisfactory edge forming accuracy.
In either case, the cutting operation is required to be conducted such that the cutting volume is relatively small since the apparatus must be movable at the job site. In addition, it is necessary to machine the lip with high accuracy to ensure stable welding of a root pass on a pipe. However, it is difficult for a conventional edge-preparing apparatus to realize such high-accuracy machining. Therefore, accuracy is improved by hand work polishing after machining. However, this is labor-consuming, and there is still great difficulty in obtaining the desired accuracy.
In view of the above-mentioned problems, objects of the present invention are to provide an improved cutting apparatus and to provide a profile machining apparatus in which the cutting tool has a small contact area and an edge profile of a pipe may be readily formed in any shape with high accuracy.